There is a continuing demand for improvements in water closets, and one area of particular concern is the amount of water used during each flushing cycle. There are already laws or regulations in various areas of the country setting maximum water usage limits, and it is expected that such requirements will increase and become ever more strict. One area where improvements in the typical water closet can be made is the flush valve. Most water closets in use today have the conventional type of ball flush valve where the valve is lifted by a chain or other linkage with the operating handle and then drops back onto its seat as the water level in the tank lowers. While most such arrangements are generally satisfactory, every homeowner is aware of the problems that arise when the ball valve wears, fails to seat properly, etc. More importantly, however, such valves are not particularly efficient from the standpoint of providing adequate flushing with minimum water usage, one of the problems in this regard being that the flow rate through the tank outlet tends to decrease as the water level in the tank lowers. Conventional flush valves present particular problems in so-called "one piece" water closets where the tank is lower so there is less of a pressure head.
The foregoing problems can be solved by the use of a siphon-type flush valve with a water supply jet that feeds into the upleg to develop a siphonic action that quickly empties the water from the tank into the bowl. Valves of this type are not new as such - see for example U.S. Pat. Nos. 952,101; 1,259,226; 1,593,336; 2,073,835; 2,412,691; 3,750,195 and 3,773,063 - but known valves of this type are not fully satisfactory from all standpoints. It is, for example, desirable to have the supply jet operative during the entire time the tank is emptying and then use the same jet to supply water for refill, but it is difficult to provide simple and reliable means for diverting the flow from the upleg toward the tank at the conclusion of the flushing portion of the cycle.
Another problem is providing a satisfactory rim wash, again using a minimum quantity of water. There are arrangements in which a fresh water jet feeds the rim and also aspirates tank water toward the rim to provide a better washing action -- see for example U.S. Pat. No. 3,172,128 -- but, again, it is desirable to be able to divert the rim flow to refill after the flushing part of the cycle has been completed, and it is difficult to provide simple and reliable means for doing so.